Anthelmintic closantel enhances bacterial killing of polymyxin B against multidrug-resistant Acinetobacter baumannii

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Polymyxins, an old class of antibiotics, are currently used as the last resort for the treatment of multidrug-resistant (MDR) Acinetobacter baumannii. However, recent pharmacokinetic and pharmacodynamic data indicate that monotherapy can lead to the development of resistance. Novel approaches are urgently needed to preserve and improve the efficacy of this last-line class of antibiotics. This study examined the antimicrobial activity of novel combination of polymyxin B with anthelmintic closantel against A. baumannii. Closantel monotherapy (16 mg l−1) was ineffective against most tested A. baumannii isolates. However, closantel at 4–16 mg l−1 with a clinically achievable concentration of polymyxin B (2 mg l−1) successfully inhibited the development of polymyxin resistance in polymyxin-susceptible isolates, and provided synergistic killing against polymyxin-resistant isolates (MIC 4 mg l−1). Our findings suggest that the combination of polymyxin B with closantel could be potentially useful for the treatment of MDR, including polymyxin-resistant, A. baumannii infections. The repositioning of non-antibiotic drugs to treat bacterial infections may significantly expedite discovery of new treatment options for bacterial ‘superbugs’.

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This study is supported by a research grant from the National Institute of Allergy and Infectious Diseases of the National Institutes of Health (R01AI111965) awarded to JL, TV, JNS, AF, AWP and DJC. YD is supported in part by R01AI104895. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Allergy and Infectious Diseases or the National Institutes of Health. JL and AWP are Australian National Health and Medical Research Council (NHMRC) Senior Research Fellows. TV is an Australian NHMRC Industry Career Development Research Fellow and DJC is an Australian NHMRC Career Development Research Fellow.

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Correspondence to Jian Li.

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